Recently, various flat display devices have been actively studied and researched: for example, liquid crystal display (LCD) devices, field emission display (FED) devices, electro-luminescence display (ELD) devices, and plasma display panels (PDP). Among the flat display devices, the LCD device has been generally used for notebook PCs, desktop monitors and liquid crystal televisions. The LCD device has a high contrast ratio, good gray scale, high-quality moving picture image, and low power consumption.
As shown in FIG. 1, an LCD panel 70 includes an upper substrate 101 provided with a color filter layer 112 to represent various colors; a lower substrate 102 provided with a switching element to change the alignment of liquid crystal molecules; and a liquid crystal layer 100 provided between the upper substrate 101 and the lower substrate 102.
In addition to the color filter layer, the upper substrate 101 includes a black matrix 111 which prevents light leakage; and a common electrode 113 which applies a voltage to the liquid crystal layer 100. The lower substrate 102 includes a pixel electrode 122 as well as a switching element. In this case, the switching element is formed of a thin film transistor 121, and the pixel electrode 122 applies a voltage to the liquid crystal layer 100 in response to a signal outputted from the thin film transistor 121.
A spacer 115 is provided between the upper and lower substrates 101 and 102, and the spacer maintains a predetermined gap between the upper and lower substrate 101 and 102. Around the circumference of the substrate, there is a sealant 116 to prevent the liquid crystal 100 from flowing out.
The LCD panel does not itself emit light. Thus, the LCD device requires an additional light source. For a transmitting type LCD device, an additional light source, for example, a backlight assembly to emit and guide the light is provided.
The backlight assembly may be classified into an edge type and a direct type based on a transmission mode of light.
For the edge-type backlight assembly, a cylindrical line-type light source such as a light-emission lamp (hot cathode or cold cathode) is provided at a lateral side of an LCD panel, so that the light emitted from the light-emission lamp is transmitted to an entire surface of the LCD panel through the use of a transparent light-guiding plate. In case of the direct-type backlight assembly, light-emission lamps are provided under the LCD panel, and are selectively driven, so that the light emitted from the light-emission lamps is diffused to an entire surface of an LCD panel through the use of a light-diffusion plate provided between the light-emission lamps and the LCD panel.
The edge-type backlight assembly is problematic in that it is insufficiently competitive owing to the complicated and complex part sourcing and assembling process. Furthermore, after assembling the lamp into a lamp-housing, the light may leak. Also, the brightness is lowered since the light passes through the light-guiding plate.
To overcome these problems of the edge-type backlight assembly, the direct-type has been proposed, in which the light-emission lamps are selectively provided under the LCD panel, to realize high brightness and uniform luminosity.
For a large display area, it is necessary to provide the light source of uniform luminosity. In this respect, it is preferable to provide the direct-type backlight assembly.
In order to realize the backlight assembly of high brightness by the direct type, a plurality of light-emission lamps may be provided under the display screen, or one light-emission lamp having a bent structure may be provided.
FIG. 2 is an exploded perspective view of illustrating a related art backlight assembly. FIG. 3 is a cross section view along I-I′ of FIG. 2. FIG. 4 is a perspective view of illustrating a related art lamp guide 60.
As shown in FIGS. 2 and 3, the direct-type backlight assembly includes a plurality of light-emission lamps 51 which emit the light; a reflecting plate 52 which reflects the light emitted from the lamps 51 toward an LCD panel (not shown); a light-diffusion plate 55 which is provided above the light-emission lamps 51; optical sheets 56 which are comprised of a light-diffusion sheet and a prism sheet; a case 53 which fixes and supports the various elements including the light-emission lamps 51; and a bezel 71 of stainless steel which is provided on the circumference of the LCD panel to surround the circumferential part except for an effective area to display images.
A lamp guide 60 which is provided inside the case 53 maintains a predetermined gap between the light-emission lamps 51 and the reflecting plate 52; and support sides (not shown) which are provided at both ends of each light-emission lamp 51 to support and fix each light-emission lamp 51.
The lamp guide 60 supports the light-emission lamps and prevents the light-diffusion plate 55 and the optical sheets 56 from sagging. The support side fixes the light-emission lamp 51, and stably maintains the light-diffusion plate 55 and the optical sheets 56 thereon.
The lamp guide 60 is provided in the space between the light-diffusion plate 55 and the reflecting plate 52. As shown in FIG. 4, the lamp guide 60 is comprised of a supporter 61 which contacts and supports the light-diffusion plate 55; and holders 62 which are provided to fix and support the light-emission lamp. The supporter 61 of the lamp guide is formed in a conical structure having a fixed height, so that the height of the supporter 61 is does not change, even though an external force is applied thereto.
The light emitted from the light-emission lamps 51 is transmitted to the display area through the light-diffusion plate 55 and the optical sheets 56.
In the direct-type backlight assembly, the light-diffusion plate is formed of polymer material. In this case, if an external force is applied to the LCD device, or the LCD device is distorted, the light-diffusion plate may be moved upward or downward. Thus, whenever the light-diffusion plate contacts the supporter, a distortion occurs due to the contact force therebetween. Also, the scratches may occur in the light-diffusion plate since the supporter of the lamp guide is stronger than the light-diffusion plate. Thus, the light is not diffused in the scratched areas of the light-diffusion plate, and the image may be blurred.